Electrochemical cells are commonly used as electrical energy sources. Generally, a cell contains a negative electrode and a positive electrode. The negative electrode contains an active material (e.g., zinc particles) that can be oxidized; and the positive electrode contains an active material (e.g., manganese dioxide) that can be reduced. The active material of the negative electrode is capable of reducing the active material of the positive electrode. In order to prevent direct reaction of the active material of the negative electrode and the active material of the positive electrode, the electrodes are electrically isolated from each other by a separator.
When a cell is used as an electrical energy source in a device, electrical contact is made to the electrodes, allowing electrons to flow through the device and permitting the respective oxidation and reduction reactions to occur to provide electrical power. An electrolytic solution (e.g., a potassium hydroxide solution) in contact with the electrodes contains ions that flow through the separator between the electrodes to maintain charge balance throughout the cell during discharge.
In one type of electrochemical cell, called a metal-air cell, oxygen is reduced at the positive electrode, and a metal is oxidized at the negative electrode. Oxygen can be supplied to the cathode from the atmospheric air external to the cell through one or more air hole(s) in a cell housing.